Developmental regression is a complex phenomenon which occurs in 20-49% of the autistic population. Aim of the study was to assess possible differences in the development of regressed and non-regressed autistic preschoolers. We longitudinally studied 40 autistic children (18 regressed, 22 non-regressed) aged 2-6 years. The following developmental areas were considered fundamental in the first years of life, and were assessed at ages 2, 3, 4, 5, and 6: receptive and expressive language, communicative and request modalities, play activities, and mental age. Children who regressed showed lower mean performances than those who did not regress and, in the time intervals considered, non-regressed children improved their ratings in the above mentioned variables significantly more than regressed children.